Underwater firing mechanism



Patented Dec. 1, 1953 UNITED STATES PATENT OFFICE (Granted under Title35, U. S. Code (1952),

see. 266) 7 Claims.

This invention relates to firing mechanism and more especially toimprovements in safety means for firing mechanisms employed insubmersible explosive bodies.

One of the primary requisites in the construction of explosives bodiesis to so design the firing mechanism that it will not accidentally beset in operation to cause an explosion of the body pre maturely, thatis, while it is being handled preparatory to use and even moreimportant, so that it will not be set in operation even thoughmishandled. In the present instance, the invention is concernedspecifically with an explosive device adapted to be used in minesweepingoperations and upon contact with the cable of an opposing mine toexplode, thereby to cut the cable and free the mine so that it will riseto the surface. Such devices receive rather rough handling While as yetunsubmerged, that is, preparatory to use in the sweeping operation andwhile they are provided with safety pins which prevent operation of thefiring pin mechanism unless withdrawn, there is no guarantee that thepin will not accidentally or unwittingly be removed before the device issubmerged, or that through falling from a height and striking the deckor other object the inertia of the firing pin itself will not besuflicient to cause penetration of the primer, thereby igniting it andcausing serious injury to personnel.

It is an object of this invention to provide an explosive body, thefiring mechanism of which will not cause an explosion of the body eventhough set in operation as long as the body is unsubmerged, and of suchconstruction that if dropped the inertia of the firing pin will notpenetrate the primer.

To this end invention resides in a firing mechanism including a firingpin of very light weight, a firing plunger having a normally emptychamber therein associated with the firing pin and adaptedtelescopically to fit over an end of the firing pin without makingcontact therewith, and hence, without actuating the same as long as onlyair occupies the chamber, but adapted when liquid is trapped in thechamber between it and the firing pin to transmit the impulse of theplunger through the liquid to actuate the firing pin. More specifically,as illustrated herein, the mechanism comprises a hollow cylindricalbody, a plug having a reduced portion threaded into one end thereofhaving a central bore therein, a primer disposed in the bore, a firingpin disposed in the bore adjacent to the primer, a shear pin arranged toretain the firing pin in spaced relation to the primer, a plunger havinga cup shaped head adapted to fit over the end of the reduced portion ofthe plug to form a closed chamber, means for limiting the movement ofthe plunger so that it does not contact the firing pin and will nottransmit its motion thereto, except through the intermediary of thewater trapped therein, a spring adapted to move the plunger toward thefiring pin and a removable release pin arranged manually to restrain theplunger but upon removal to permit it to be driven toward the firingpin.

It is a further object of this invention to provide a firing mechanismwhich, when actuated, will bring about ignition of the primer eventhough it is saturated with water, that is, regardless of whether it isdry or wet.

In this aspect invention resides in means for causing the firing pin topenetrate the primer at high velocity, thereby to generate frictionalheat between the firing pin and the primer charge to cause ignition ofthe primer even though it is saturated with water. As illustratedherein, this is attained by constructing the plunger so that it traps avolume of water between it and the firing pin, the area of the plungerbeing far in excess of the area of the firing pin, hence, multiplyingthe movement of the plunger and resulting in greatly magnifying themovement of the firing pin. Specifically, the ratio of the diameter ofthe plunger to that of the firing pin is about 2 to l which results in aratio of 1 to 4 in the movement transmitted from the plunger to thefiring pin. With an initial velocity of about 20 feet per second,produced by a spring adapted when released to drive the plunger towardthe firing pin, by reason of the aforesaid multiplication of motion, thefiring pin is caused to move approximately feet per second into theprimer.

The invention will now be described in detail with reference to theaccompanying drawing, in which:

The single figure shows a section through my improved safety device.

Referring to Fig. 1,'the safety firing mechanism indicated generally byreference character I0 comprises a hollow cylindrical body 12 having achamber l4 therein which extends from one end throughout the greaterportion thereof and a guide-Way l6 forming a continuation of the chamberto the other end, the guide-way being of smaller diameter than thechamber. The chamber I4 is provided with internal threads 18 near theopen end thereof, and into this open threaded end there is screwed aplug 2|] having a, reduced inwardly projecting extension 22. The

plug is provided with a longitudinal bore 24,

the inner portion of which is enlarged at 26 so that a peripheralshoulder 28 is formed substantially midway between the ends of the bore25. In the enlarged portion 26 of the bore, there is disposed a primer30 which is seated against the shoulder 28 and a firing pin 32 which isspaced inwardly from the primer and is retained in spaced relationthereto near the inner end of the bore by a shear pin 34 passing throughit and the walls of the extension 22. The firing pin is made light inweight so that it has little inertia and hence is insensitive to asudden change in the motion of the device. This feature adds to thesafety of the device since the firing pin will not be caused to backaway if the device is dropped, even though as much as thirty or fortyfeet. A plurality of radially disposed passages 36 are formed in thisportion of the cylindrical body I2 extending from the outward sidethereof inwardly through the walls and through a portion of the plug 2d,the passages terminating in the enlarged portion 26 of the bore betweenthe primer 30 and the firing pin 32. The passages 36 are inclineddownwardly. There is also disposed in the chamber I4 inwardly of theextension 22, a plunger 33 having an enlarged head thereon which isadapted to fit the inside of the chamber I l and to slide longitudinalltherein, the head being guided in its longitudinal movement by the closefit of the plunger in the guide-way IS. The head 40 of the plunger isrecessed at M and the inside diameter of the recess ll is adaptedtelescopically to fit over the inwardly projecting extension 22. Themovement of the plunger is limited by contact of the peripheral edge 42of the head with a peripheral shoulder 44 formed near the base of theextension 22. The depth of the aforesaid recess is such that when theplunger has reached the aforesaid limit of movement the bottom of therecess willnot engage the end of the firing pin 32-. To make doubly surethat there will be no such contact between the bottom of the recess andthe end of the firing pin, the firing pin preferably is disposed at somelittle distance inwardly in the bore 26 formed in the extension 22. Theplunger 38 is urged toward the extension 22, and hence the firing pin,by a coiled spring 48 which is disposed about the body of the plunger38, between a shoulder 50 formed at the rear side of the head 0 and ashoulder 52 formed between the intersection of the chamber M with theguide-way Hi. The plunger 38 is held in a retracted position with thespring 48 compressed by a removable release pin 54 which is passedthrough diametrically disposed openings 56 formed near the end of thebody i2 and a diametrical passage 58 formed near the end of the plunger.To admit water to the chamber 14 when the device is submerged, anopening 43 is provided in the wall of the body l2.

In underwater firing mechanism, it is as a, practical matter, difficultto keep the primer dry, and when the primer is damp or wet, a misfirewill result upon actuation of the firing mechanism. In such case thefiring pin may penetrate the primer mixture, but because of itscomparatively low velocity and the moisture present, no ignition takesplace. If, however, a firing pin is driven into a primer mixture withsufiiciently high velocity, heat is developed in sufiicient quantity tocause ignition of the primer even though it is saturated with water.While the required velocity could be attained by use of mechanical meanssuch as the spring 48 shown in Fig. 1, a sprin of the strength requiredto impartjthe itessary velocity would be large, and hence, it w' d makethe device bulky. Moreover, it would be hard to handle a spring of suchstrength and stillness in assembling the device. To avoid this, {and yetto attain the desired velocity, the'jhydraulic means consisting of theplunger 16 and'i ts head 40, together with the firing pin 32 and bore 26is so designed that the movement of the plunger is greatly magnifiedthrough the intermediary of the water trapped between the recess ain thehead 40 and the firing pin to impart the jhigh velocity to the firingpin. As shown herein, the ratio of the diameters of the recess Hijin theplunger to the diameter of the bore 26 andhence of the firing pin isabout 2 to 1. Specifically, the diameter of the recess 4! is /2 inch andthediameter of the firing pin is /4. inch. With the spring 48 designedto impart a velocity of 20 ft per second to the plunger and a ratio of 2to 1 described, the firing pin will be caused totrav'el at a speed offeet per second. Thisjspeed is great enough to cause the firing pin topenetrate the primer with sufficient velocity to ignite the primer eventhough it is wet. While a somewhatsmaller ratio of diameters may beemployed with success for the ignition of a primer, it is best to employa ratio which will give sufficient velocityi to the firing pin to causepenetration of the primer, and simultaneously, generation of frictionalheat of sufiicient intensity to cause ignition under the most adverseconditions. With this in view, the invention contemplates ratio whichwill, give a. speed up to about 500 feet per second-to-insure ignitioneven when the primer has been exposed for long periods, to sea water.

In normal use, the safety pin 54',is inserted in place to hold theplunger retracted during assembly and is left in the device when it issubmerged for a minesweeping operation. A line is attached to the pinwhich will be caused to withdraw the pin when an opposing mine cablecomes into contact with the device thereby to release the'plunger. It isobvious, however, that in preparation for using the device this pin mayaccidentally be removed and if this should happen the plunger 38 wouldbe driven forward by the coiled spring 48 with considerable force. Asconstructed, if this happens, the recess 4] will slide over the end ofthe extension 22 and as long as the device is unsubmerged, and only airis present in the recess after it begins to move over the end of theextension 22, the compression of the air which results from thepiston-like action between the extension 22 and the head 40 will not besufiicient to shear the shear pin 34 and drive the firing pin into theprimer 30. This, it is obvious, will, therefore, insure againstaccidental firing of the device as long as it is unsubmerged even thoughthe release pin is accidentally or otherwise removed. As soon as thedevice is submerged, however, water flows into the body 12 through theopening 43, filling the chamber I4. If now, the release pin 54 isremoved, the recess 4| of the head 40 in its forward movement traps abody of water between it and the extension and the resultant pressuredeveloped and hydraulically transmitted through the intermediary of thewater to the end of the firing pin, is sufficient to shear the shear pin34 and to drive the firing pin 32 at high velocity into the primer 30,and hence, to explode the body, even though the primer is saturated withwater. In order to relieve the water pressure between the firing pin andthe primer and to permit the water therein readily to escape,

there is provided the radial passages 36, heretofore described.

The invention described herein may be manufactured and used by or forthe Government of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

What is claimed is:

1. In a firing mechanism, a hollow cylindrical body, a firing pinslideably mounted in a tubular plug having a reduced end and positionednear one end of the hollow body, a plunger in said hollow body adaptedto slide longitudinally therein toward firing pin, means for urging theplunger toward the firing pin, removable means for restraining theplunger, a cup shaped head on said plunger adapted to slide over thereduced end of the tubular plug, upon longitudinal movement thereof whensaid means for restraining the plunger is removed, without contactingsaid firing pin adapted to transmit its motion to the firing pin onlywhen a liquid is trapped in the cup formed between said cup shaped headand the reduced end or" said tubular plug slideably holding said firingpin.

2. In a firing mechani m, a hollow cylindrical body, a plug threadedinto one end thereof, said plug having a central bore therein, a primerin said bore, a firing pin adjacent thereto, a plunger mounted forsliding movement in said cylindrical body toward the firing pin, aspring normally urging said plunger toward said firing pin, a removablerelease pin restraining the plunger from movement, a cup shaped head onthe plunger adapted to fit over the inner end of the plug to form aclosed chamber to trap air or water between it and the firing pin, saidchamber being so designed that if said release pin is withdrawn whilethe mechanism is as yet unsubmerged the pressure created by thecompression of the air between the head and the firing pin will not besufficient to actuate the same.

3. In a firing mechanism, a hollow cylindrical body, a plug threadedinto one end thereof, said plug having a central bore therein and aninner reduced end, a primer disposed in the bore, a firing pin disposedin the bore adjacent to the primer, a shear pin retaining the firing pinin spaced relation to the primer, a plunger having a cup shaped headadapted to fit over the end of said reduced portion to form with saidreduced portion a closed chamber, the volume of which may beprogressively reduced, means for limiting the movement of the plunger sothat it does not make contact with the firing pin and hence will nottransmit its motion thereto except through the intermediary of watertrapped therein, a, spring adapted to move the plunger toward the firingpin, and a removable release pin arranged manually to restrain theplunger but upon release to permit it to be driven toward the firingpin.

4. In a firing mechanism, a hollow cylindrical body, a plug threadedinto one end thereof, said plug having a central bore therein, a primerin said bore, a firing pin adjacent thereto but spaced therefrom, reliefpassages extending from the exterior of said body into the space betweenthe primer and the firing pin, a plunger mounted for sliding movement inthe cylindrical body to ward the firing pin, a spring normally urgingthe plunger toward the firing pin, a removable release pin restrainingthe plunger from movement, and a cup shaped head on the plunger adaptedto fit over the inner end of the plug to form a closed chamber to trapair or water between it and the firing pin, said chamber being sodesigned that if said release pin is withdrawn while the mechanism is asyet unsubmerged the pressure created by the compression of the airbetween the head and the firing pin will not actuate the same.

5. A firing mechanism for an explosive cutter, comprising a body havinga chamber therein one end of which is open, a firing pin slidablymounted in a tubular plug having a reduced end and positioned in theopen end of the chamber, a plunger in said chamber behind the firing pinadapted to slide longitudinally therein toward the firing pin, means forurging the plunger toward the firing pin, removable means forrestraining the plunger, a cup-shaped head on said plunger adapted toslide over the end of the reduced end of said tubular plug having thefiring pin therein, upon longitudinal movement thereof when said meansfor restraining the plunger is removed, without contacting said firingpin and adapted to transmit its motion to the firing pin only when aliquid is trapped between it and n end of the firing pin in the spaceformed by the cup shaped head and the reduced end of said plug 6. Afiring mechanism for an explosive cutter employed in mine sweepingcomprising a body having a chamber therein, one end of which is open, afiring pin and means for mounting the same in the open end of thechamber, said means including a tubular plug fitting over said firingpin and having a reduced end, a plunger in said chamber behind thefiring pin adapted to slide longitudinally thereof toward the firingpin, means for guiding the plunger in its movement, means for urging theplunger toward the firing pin, removable means associated with theguiding means for restraining the plunger, a cupshaped head on saidplunger adapted to slide over the reduced end of said tubular plugfitting over the firing pin, upon longitudinal movement thereof whensaid means for restraining the plunger is removed, without contactingsaid firing pin and adapted to transmit its motion to the firing pinonly when a liquid is trapped in the cup between it and the end of thetubular plug.

7. A firing mechanism for an explosive cutter, comprising a body havinga chamber therein, one end of which is open, said chamber having anaperture in its wall to admit water thereto when said body is submerged,a plug having a central bore therein threaded into the open end of thechamber, a primer in said bore, a firing pin adjacent to said primer, aplunger mounted for sliding movement in said chamber toward said firingpin, a spring normally urging said plunger toward said firing pin, aremovable release pin restraining the plunger from movement, a cupshapedhead on the plunger adapted to fit over the inner end of the plug toform a closed pocket to trap air or water between it and the firing pin,said pocket being so designed that if said release pin is withdrawnwhile the body is as yet unsubmerged the pressure created by thecompression of the air between the head and the firing pin will not besufiicient to impart movement to said firing pin.

HENRY H. MOI-IAUPT.

m References Cited in the file of this patent UNITED STATES PATENTSNumber Name Date 1,092,702 Elia Apr. '7, 1914 1,313,546 Lander Aug. 19,1919

